Basic PoC for callgraph generation

[OmkarPh]

Fixes #3

I'm using // as separator for namespaces. Please suggest anything else if get any collision with any programming language's syntax features

I've not put example python files under fixtures to just keep the namespaces (starts with fileName) short when debugging
Also, some things like 'init' , '.' for base identifier are still present, need to generalise those
Also, there's a lot of debug residue, will get it cleaned up once we finalise on the approach

Try -

cd examples/plugin/callgraph

# works
go run main.go -dir testScopes.py
go run main.go -dir testNestedFn.py
go run main.go -dir testObjAssignment.py
# here, we have a false positive, if an identifier was assigned to two different classes
# it doesn't just show latest assignment, but all of them, need to discuss on this more
# eg. if x=ClassA() and then x=ClassB() is conditionally assigned (can't evaluate dynamic if elses),
# then its better to have all possibilities ?

# this doesn't work -
go run main.go -dir testFnAssignment.py
# here, xyz() resolves to both foo() and bar()

go run main.go -dir testClass.py
# partially works, but higher order 'func' isn't taken care of
# also, "Hello, World!".encode('utf-8') isn't taken care of